One hundred sixty-eight patients with hand tendon injuries were randomized to receive either ultrasound-guided postoperative CMC hydrogel injection (n=84) or intraoperative hydrogel application (n=84). The primary outcome was total active motion (TAM) at 12 months. Secondary outcomes included visual analog scale (VAS) pain scores, Michigan Hand Outcomes Questionnaire–Activities of Daily Living (MHQ-ADL), and MHQ satisfaction scores. Follow-up assessments occurred at 3 weeks, 6 weeks, 3 months, 6 months, and 12 months. Overall, the results revealed that the postoperative injection group had significantly greater improvements in TAM, better early pain relief, and higher MHQ-ADL scores. These findings suggest that ultrasound-guided postoperative hydrogel injection enhances functional recovery and early pain control more effectively than intraoperative application.